1. Field of the Invention
This invention relates to the production of new isocyanate prepolymers and to their use as the principal component in moisture-hardening sealing compounds, adhesives, and coating compositions.
2. Statement of Related Art
The use of NCO-terminated polyurethane prepolymers in adhesives, coating compounds, lacquers, etc. is known. These onecomponent systems harden through reaction of the NCO groups with atmospheric moisture, three-dimensional networks being built up. An alternative to this hardening principle is the addition of masked amines which do not react with the isocyanate groups in the absence of moisture, but which in the presence of moisture release amino groups which bring about the crosslinking reaction with the NCO groups.
The disadvantage of all moisture-hardening polyurethane systems is their tendency to form microcracks and bubbles through the release of carbon dioxide during hardening. This effect is regarded as troublesome in virtually every field of application. Although the formation of bubbles is avoided by addition of the masked hardeners mentioned above (ketimines, aldimines), these systems have serious deficiencies in regard to their storability. Even traces of moisture are sufficient to demask the amine, so that crosslinking occurs before the composition is applied. In addition, the adhesion of systems of this type to various substrates is often inadequate, so that in practice the surfaces have to be pretreated or rather primed.